U.S. patent number 5,314,952 [Application Number 07/659,352] was granted by the patent office on 1994-05-24 for processes for producing highly water absorptive resins.
This patent grant is currently assigned to Lucky, Ltd.. Invention is credited to Su B. Choi, Tae H. Jang, Myung J. Kim, Huyng M. Lee.
United States Patent |
5,314,952 |
Choi , et al. |
May 24, 1994 |
Processes for producing highly water absorptive resins
Abstract
The processes for producing highly water absorptive resins of
the present invention comprise the following steps: (A) suspending
an aqueous solution of partially neutralized alkali metal acrylate
and optionally partially neutralized acrylamido alkane sulfonate in
a hydrocarbon solvent containing a surfactant having a HLB value of
3.apprxeq.6 or 8.apprxeq.12; (B) subjecting the mixture to inverse
suspension polymerization in the presence of at least one water
soluble radical polymerization initiator; (C) if necessary,
separating the moisture from the produced polymer by azeotropic
distillation to reduce the water content to about 15 to 55% by
weight; (D) adding a crosslinking agent having two or more reactive
groups such as epoxy groups, if desired, as a solution form to
subject the surface of the polymer to crosslinking reaction; and
optionally (E) subjecting to coagulation with the use of a
coagulant in the presence of an inert solvent, whereafter drying
the resultant coagulate to obtain the water absorptive resin.
Inventors: |
Choi; Su B. (Daejeon,
KR), Lee; Huyng M. (Daejeon, KR), Kim;
Myung J. (Daejeon, KR), Jang; Tae H. (Daejeon,
KR) |
Assignee: |
Lucky, Ltd. (Seoul,
KR)
|
Family
ID: |
27567091 |
Appl.
No.: |
07/659,352 |
Filed: |
April 22, 1991 |
PCT
Filed: |
June 08, 1990 |
PCT No.: |
PCT/KR90/00005 |
371
Date: |
April 22, 1991 |
102(e)
Date: |
April 22, 1991 |
PCT
Pub. No.: |
WO90/15829 |
PCT
Pub. Date: |
December 27, 1990 |
Foreign Application Priority Data
|
|
|
|
|
Jun 21, 1989 [KR] |
|
|
89-8596 |
Jun 21, 1989 [KR] |
|
|
89-8597 |
Jul 3, 1989 [KR] |
|
|
89-9405 |
Jul 3, 1989 [KR] |
|
|
89-9406 |
Jul 27, 1989 [KR] |
|
|
89-10672 |
Jul 27, 1989 [KR] |
|
|
89-10673 |
Oct 7, 1989 [KR] |
|
|
89-14440 |
|
Current U.S.
Class: |
525/119; 525/360;
525/366; 525/385; 526/207; 526/241; 526/317.1; 526/73 |
Current CPC
Class: |
A61L
15/60 (20130101); C08F 8/00 (20130101); C08F
8/14 (20130101); C08F 20/06 (20130101); A61L
15/60 (20130101); C08L 33/02 (20130101); C08F
8/00 (20130101); C08F 20/00 (20130101); C08F
8/14 (20130101); C08F 20/04 (20130101) |
Current International
Class: |
A61L
15/16 (20060101); A61L 15/60 (20060101); C08F
8/14 (20060101); C08F 8/00 (20060101); C08F
20/00 (20060101); C08F 20/06 (20060101); C08F
002/32 (); C08F 008/00 (); C08F 008/14 (); C08F
020/06 () |
Field of
Search: |
;575/119,385
;526/73 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Zitomer; Fred
Attorney, Agent or Firm: Townsend and Townsend Khourie and
Crew
Claims
What is claimed is:
1. A process for producing a highly water absorptive amorphous
resin, which comprises
(a) suspending an aqueous solution of partially neutralized alkali
metal acrylate wherein about 50 to 100% by mole of the carboxyl
group has been neutralized to its alkali metal salt and at least
one water soluble radical polymerization initiator, in a
hydrocarbon solvent containing a surfactant having a HLB value of
8.about.12;
(b) subjecting the mixture to inverse suspension polymerization
while raising the internal temperature of the reactor successively
to 70.degree. C., to 60.degree..about.67.degree. C., and then to
75.degree. C., to undergo phase-transition;
(c) during or after the polymerization, separating the moisture
from the produced polymer by azeotropic distillation to reduce the
water content to about 15 to 55% by weight, and filtering to remove
the solvent;
(d) adding a crosslinking agent having three or more reactive epoxy
groups which is dissolved in methanol, wherein the amount of the
crosslinking agent is 0.005.about.15% by weight based on the
produced polymer, and incubating for 1.about.2 hours at
temperatures 70.degree. to 85.degree. C.; and
(e) washing with methanol, filtering, and drying at temperatures of
90.degree. to 175.degree. C. to obtain the water absorptive
resin.
2. The process according to claim 1, wherein the surfactant is
sorbitan monolaurate or Ryoto Sugar Ester S-970.RTM..
3. The process according to claim 1, wherein the hydrocarbon
solvent is selected from the group consisting of n-hexane,
n-heptane and cyclohexane.
4. The process according to claim 1, wherein the hydrocarbon
solvent is cyclohexane.
5. The process according to claim 1, wherein the water soluble
radical polymerization initiator is selected from the group
consisting of ammonium persulfate, potassium persulfate and
hydrogen peroxide.
6. The process according to claim 1, wherein the water soluble
radical polymerization initiator is potassium persulfate.
7. The process according to claim 1, wherein the crosslinking agent
is selected from the group consisting of glycerol polyglycidyl
ether, trimethylol propane polyglycidyl ether and sorbitol
polyglycidyl ether.
8. The process according to claim 1, wherein the partially
neutralized alkali metal acrylate is prepared by addition of an
alkali metal hydroxide such as sodium hydroxide, lithium hydroxide
or potassium hydroxide.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to processes for producing highly
water absorptive resins having excellent water absorbency and
saline solution absorbency. More particularly, it relates to
processes for producing highly water absorptive resins having a
high water absorption rate and water absorptive capacity, and an
excellent gel-strength.
2. Description of the Prior Art
Various water absorbing materials such as sponge, pulp, paper and
the like, are well known in the art. Also various synthetic
products made by graft polymerization of materials containing a
hydrophilic group, such as --OH, --NH.sub.2, --COOH, and the like,
have been used conventionally. However, such water absorbing
materials, e.g. a sponge, a pulp, and a paper, are characterized
with physical mechanisms for absorbing water so that such materials
have defects in that the majority of the absorbed water can be
easily squeezed out by the application of external pressure. In
recent years, in order to solve these defects, synthetic
water-absorptive products having particular physical and chemical
characteristics have been developed. The majority of such synthetic
products are crosslinked polyacrylic acid salts, polymethacrylic
acid salts, crosslinked polyacrylic acid-methacrylic acid copolymer
salts, crosslinked saponification products of starch-acrylonitrile
graft copolymer, and cellulose and acrylate-grafted copolymer. Such
grafted products are on the market as sanitary napkins, sanitary
pads, and diapers in the sanitary field, water absorbing containers
in the civil and gardening field, and anti-dewdrop agents in the
construction field.
However, although saponificated products of starch-acrylonitrile
graft copolymer have a relatively high deionized water-absorbency,
the saline-solution thereof is poor. Also, long-term storage is
impossible due to the main component being starch.
On the other hand, partially crosslinked polyacrylic acid salts
have high water absorption rates and capacity in saline solution as
well as in deionized water, and they can be stored for a long
period of time. Particularly, commercially available alkali metal
acrylates are used as a starting material to prepare a water
absorptive resin in the present invention.
Various processes are known for polymerizing acrylic acid and
alkali acrylate, including bulk polymerization, aqueous solution
polymerization, spray polymerization, inverse emulsion
polymerization, inverse suspension polymerization, and the like.
With the exception of inverse emulsion polymerization and inverse
suspension polymerization, it is difficult to remove the heat of
polymerization, and the viscosity of the polymerization mixture
becomes too high to carry out general polymer production. Moreover,
according to these processes it is difficult to obtain particulate
polymers.
An example of the inverse emulsion polymerization process is
disclosed in U.S. Pat. No. 3,284,393. When, for example, acrylic
acid is used as the starting material, the obtained polymer is
insoluble in water and does not have such an absorbency that the
polymer can be called a water absorptive resin even if it is
neutralized with an alkali such as sodium hydroxide or the
like.
As a process for producing an acrylic acid-alkali metal acrylate
polymer having a water absorbency, the inverse suspension
polymerization process is mentioned in Japanese Patent Publication
No. 79-30710. According to this process, a water absorptive polymer
is prepared through a stable reaction by the use of a sorbitan
fatty acid ester having a HLB (Hydrophilic-Lipophilic Balance)
value of 3.about.6. The resin thus obtained has a high deionized
water absorbency corresponding to 400.about.500 times its own
weight; however, the saline solution-absorbency of said water
absorptive resin is as low as 35.about.50 times its own weight.
In U.S. Pat. No. 4,497,930, there is disclosed a method for
producing a water absorbent polymer comprising the steps of
subjecting acrylic acid and sodium acrylate to polymerization in
the presence of a sorbitan fatty acid ester having a HLB value of
3.about.6 as a dispersing agent, and adding a crosslinking agent
with stirring in methanol to crosslink the surface of the resulting
polymer. However, a disadvantage is that the water absorptive resin
prepared by this method is unsatisfactory in water absorptive
capacity because the polymerization reaction is carried out at
temperatures too low (70.degree.-75.degree. C.) to stabilize the
reaction.
In general, a highly water absorptive resin requires good water
absorption rate, water absorptive capacity and gel-strength. These
characteristics exhibit mutually opposing correlations with each
other; therefore, some characteristics are partially sacrificed in
order to improve other characteristics.
The foregoing three properties, namely the water absorptive
capacity, the water absorption rate and the gel-strength in the
water absorbent resin, are influenced by many factors such as a
polymer particle's size and shape, the kinds of crosslinking agent
and dispersing agent used, CMC (Critical Micelle Concentration),
polymerization temperature, and so on.
In the inverse emulsion polymerization and the inverse suspension
polymerization W/O systems, it is known that the use of a
surfactant having a HLB value of 3.about.6 produces a stable
system. But according to these polymerization reactions, the
resultant particles are too minute and have many hydrophobic groups
in their surface, such that the particulate polymer is swollen too
slowly when contacted with water. Consequently, the water
absorption rate and the water absorptive capacity become
deteriorated. To solve the foregoing problem, a surfactant having a
HLB value of 8.about.12, which is known to be unstable in the
inverse emulsion and suspension polymerization systems, may be
used. However, another problem, reaction control, arises due to
agglomeration.
On the other hand, U.S. Pat. No. 4,340,706 discloses a water
absorbent resin suitable for usages which require stability in the
fluid-absorbed state for long periods of time. However, even the
resin obtained by this method is insufficient in its rate of water
absorption due to a lack of surface-crosslinking. Furthermore, in
cases where the resin is prepared at low temperatures
(55.degree..about.60.degree. C.) using this method, undesired
residual monomers are obtained in large quantities.
Representative methods for improving the water absorption rate
include increasing the surface area of the resin (i.e. decreasing
the apparent specific gravity), crosslinking the surface of the
particulate polymer after polymerization, or adding inorganic
materials. Among the foregoing methods, the method of adding
inorganic materials such as silica is advantageous. The dispersing
rate of particulate polymer is remarkably improved and
agglomeration of polymer particles is prevented. However, there is
a disadvantage in that it is difficult to obtain the desired water
absorption rate due to a poor sedimentation rate of the particulate
polymer. When using the method of crosslinking the surface of the
particulate polymer to improve the water absorption rate, there are
also disadvantages. Minute particles which are formed tend to blow
off and to agglomerate together, making it difficult to obtain a
satisfactory water absorption rate.
SUMMARY OF THE INVENTION
The present invention resides in highly water absorptive resins and
methods for their production. Water absorptive resins having
excellent water absorption properties can be obtained by carrying
out the characteristic processes comprising the following
steps:
(a) suspending an aqueous solution of partially neutralized alkali
metal acrylate, wherein about 50 to 100% of the carboxyl groups
have been neutralized to their alkali metal salts and optionally
acrylamido alkane sulfonate wherein about 50 to 100% of the
sulfonic groups have been neutralized to their alkali metal salts,
in a hydrocarbon solvent containing a surfactant having a HLB value
of 3.about.6 or 8.about.12;
(b) subjecting the mixture to inverse suspension polymerization in
the presence of at least one water soluble radical polymerization
initiator;
(c) if necessary, separating the moisture from the produced polymer
by azeotropic distillation to reduce the water content to about 15
to 55% by weight;
(d) adding a crosslinking agent having two or more reactive groups
such as epoxy groups, if desired, as a solution, preferably in
methanol, to subject the surface of the polymer to a crosslinking
reaction; and optionally
(e) coagulating the polymer of step (d) with a coagulant in the
presence of an inert solvent and drying the resultant coagulate to
obtain the water absorptive resin.
An object of the present invention is to provide improved processes
for preparing highly water absorptive resins having excellent water
absorption properties.
BRIEF DESCRIPTION OF THE INVENTION
In order to better understand the invention reference will be made
to the accompanying drawing in which:
FIG. 1 is a microphotograph (.times.200) of the water absorptive
resin having irregular shape according to Example 27; and
FIG. 2 is a microphotograph (.times.200) of the spherical water
absorptive resin according to Comparative Example 26.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, there are provided highly water
absorptive resins and processes for preparing them.
In the present invention, the polymers used include, for example,
polyacrylic acid, polymethacrylic acid, or a copolymer thereof with
maleic acid, acrylamide, 2-acrylamido-2-methylpropylsulfonic acid,
2-methacryloylethane sulfonic acid, 2-hydroxyethyl methacrylate, or
the like in a certain proportion. The most preferred polymer is
polyacrylic acid.
The first preferred embodiment of the invention is a process for
preparing a highly water absorptive resin, which comprises the
following steps;
(a) suspending an aqueous solution of partially neutralized alkali
metal acrylate wherein about 50 to 100% by mole of the carboxyl
groups have been neutralized to their alkali metal salts and at
least one water soluble radical polymerization initiator, in a
hydrocarbon solvent containing a surfactant having a HLB value
8.about.12;
(b) subjecting the mixture to inverse suspension polymerization at
temperatures of 75.degree. to 95.degree. C.;
(c) separating the moisture from the produced polymer by azeotropic
distillation to reduce the water content to about 35 to 55% by
weight, and removing the solvent by filtration to obtain a
particulate polymer;
(d) adding a crosslinking agent that has three or more reactive
epoxy groups, that is dissolved in methanol, wherein the amount of
the crosslinking agent is 0.5.about.2.5% by weight based on the
polymer, and that conducts surface-crosslinking for 1-2 hours at
temperatures of 70.degree. to 85.degree. C.; and
(e) washing the polymer of step (d) with methanol, filtering, and
drying at temperatures of 90.degree. to 175.degree. C.
The alkali metal acrylate can be obtained by neutralizing acrylic
acid with an alkali metal hydroxide such as lithium hydroxide,
sodium hydroxide, potassium hydroxide and calcium hydroxide. The
degree of neutralization is preferably about 50.about.100% by mole,
more preferably about 65.about.80% by mole. When the degree of
neutralization is lower than about 50% by mole, the hydroxide
concentration is decreased resulting in an electronic density in
the water which is also small such that the penetration intensity
is decreased. Thus the desired highly water absorptive resin would
not be obtained. The concentration of the monomer thus produced,
i.e., the alkali metal acrylate and the unneutralized acrylic acid,
is about 20.about.70% by weight based on the total weight of the
composition and the preferred monomer concentration is about
40.about.60% by weight.
Any surfactant having a HLB value of 8.about.12 and containing many
hydrophilic groups may be used in this invention. Preferred are
sorbitan monolaurate (SPAN 20, manufactured by ICI Americas Inc.,
HLB value=8.6) and Ryoto Sugar Ester S-970.RTM. (manufactured by
Mitsubishi-Kasei Food Corporation (MFC), HLB value=9). Particularly
preferred is Ryoto Sugar Ester S-970.RTM..
In general, if a surfactant having a HLB value of 8.about.12, and
having more hydrophilic groups than hydrophobic groups, is used in
the polymerization of the water absorptive resin, the possibility
of contact with the hydrophilic monomer of the starting material is
increased. As a result, the inverse emulsion polymerization system
and the inverse suspension polymerization system become very
unstable, resulting in increased viscosity of the suspension due to
the Trommsdorff effect and a reaction which is very rapidly
progressed. Consequently, it causes both the agglomeration of
particulate polymer due to the Weigenberg effect and a rapidly
emitted heat of polymerization.
However, according to the present invention these disadvantages can
be prevented resulting in a stable polymerization system. In
addition, it is unnecessary to separately add a crosslinking agent
during polymerization. A self-crosslinking reaction and a
pseudocrosslinking reaction take place to improve greatly the
absorbency of the polymer obtained. Also, the surface of the
polymer thus obtained is crosslinked with the use of a crosslinking
agent having three or more reactive groups such as epoxy groups in
the presence of an inert solvent such as methanol, such that the
polymer absorbs the methanol containing the crosslinking agent and
becomes swollen. This allows the crosslinking agent to permeate
easily into the surface of the particulate polymer for the
surface-crosslinking reaction to take place. As a result, the water
absorption rate and gel-strength of the resin become remarkably
improved.
The water soluble radical polymerization initiators used in this
invention are well known in the art of polymer chemistry, for
example, ammonium persulfate, potassium persulfate, hydrogen
peroxide, and the like. The preferred water soluble radical
polymerization initiator is potassium persulfate. The
above-mentioned polymerization initiator may be used alone or in
admixtures of two or more.
The hydrocarbon solvent used in the present invention is an
aliphatic or aromatic hydrocarbon, which has a boiling point of
30.degree..about.200.degree. C. Examples thereof are n-hexane,
n-heptane, cyclohexane, and the like. The preferred solvent is
cyclohexane.
The surface-crosslinking agent used is one having at least three or
more reactive groups such as epoxy groups, for example, glycerol
polyglycidyl ether, trimethylol propane polyglycidyl ether and
sorbitol polyglycidyl ether, preferably glycerol polyglycidyl
ether. In crosslinking step (d), methanol is preferred as an inert
solvent for improving the surface-crosslinking effect.
The process for preparation of the highly water absorptive resin
according to the first preferred embodiment of the present
invention is described in detail as follows:
(1) Preparation of the partially neutralized alkali metal
acrylate
A reactor, equipped with a condenser, a dropping funnel and a
stirrer, is charged with acrylic acid. An alkali metal hydroxide is
dissolved in water in a beaker separately to form an alkali metal
hydroxide solution. The alkali metal hydroxide solution is fed
dropwise to the reactor through the dropping funnel while being
kept at less than 30.degree. C. This neutralizes 50.about.100% by
mole of the acrylic acid to produce an equivalent amount of an
alkali metal acrylate having the degree of neutralization of
50.about.100% by mole. When the neutralization step is conducted at
a temperature of over 45.degree. C., one of the reactants could be
polymerized.
(2) Inverse suspension polymerization step
A reactor with a condenser having a Dean-Stark trap, a
pressure-equalizing dropping funnel and a stirrer is charged with a
surfactant and a hydrocarbon solvent, and then the temperature is
raised to 75.about.95.degree. C. A mixture of the partially
neutralized alkali metal acrylate prepared in step (1) and a
water-soluble radical polymerization initiator is fed to the
reactor in small portions and polymerized completely for about 1
hour.
(3) Azeotropic distilling step
The resultant polymer contains a large amount of water so that it
is difficult for the crosslinking agent to react with the surface
of the polymer. The moisture contained in the polymer is separated
by azeotropic distillation to reduce the water content of the
polymer to about 35 to 55% by weight. When the water content is
less than 35% by weight, it is uneconomic. On the other hand, when
the water content is over 55% by weight, the effect of
surface-crosslinking is decreased. After separating the water from
the polymer, the temperature of the reactor is cooled to room
temperature. The solvent is removed by filtration.
(4) Surface-crosslinking step
The polymer produced in step (3) is crosslinked by the crosslinking
agent so as to improve water absorption rate and gel-strength. The
polymer and the crosslinking agent are dissolved in methanol and
added to a reactor equipped with a condenser, a stirrer, and a
dropping funnel. The temperature is held between 75.degree. and
80.degree. C., and the surface-crosslinking reaction is carried out
for 1 to 2 hours. The polymer thus treated is cooled to room
temperature and the methanol is removed by filtration.
(5) Washing and drying step
To remove residual monomers, the obtained polymer is washed twice
with methanol and filtered. The filtered polymer is dried at a
temperature of 90.degree. to 175.degree. C. and passed through a
50-mesh wire gauze to obtain the water absorptive resin having a
uniform size. The water absorption rate and water absorptive
capacity of the obtained resin are measured by the filtering
method.
The second preferred embodiment of the invention is a process for
preparing a highly water absorptive resin, which comprises the
following steps:
(a) suspending an aqueous solution of partially neutralized alkali
metal acrylate wherein about 50 to 100% by mole of the carboxyl
groups have been neutralized to their alkali metal salts and at
least one water soluble radical polymerization initiator, in a
hydrocarbon solvent containing a surfactant having a HLB value of
8.about.12;
(b) subjecting the mixture to inverse suspension polymerization at
temperatures of 55.degree. to 60.degree. C.;
(c) separating the moisture from the produced polymer by azeotropic
distillation to reduce the water content to about 15 to 45% by
weight;
(d) adding a crosslinking agent having three or more reactive epoxy
groups, and which is dissolved in methanol (10.about.30% by weight
based on the polymer), and subjecting the mixture to
surface-crosslinking for 1 to 2 hours at temperatures of 70.degree.
to 85.degree. C.;
(e) cooling down to room temperature and then filtering to obtain
the surface-crosslinked polymer; and
(f) subjecting to coagulation with the use of a coagulant dissolved
in methanol of 3.about.5 times by weight based on the polymer,
wherein the amount of the coagulant is 0.5.about.3.0% by weight
based on the polymer, whereafter the resultant coagulate is
dried.
The alkali metal acrylate, the surfactant, the water soluble
radical polymerization initiator, the hydrocarbon solvent and the
surface-crosslinking agent are the same as described in the
foregoing first preferred embodiment of this invention.
The coagulant is a proton-releasing acid such as sulfuric acid,
acetic acid, nitric acid, or hydrochloric acid. The preferred
coagulant is sulfuric acid.
The process for preparation of the highly water absorptive resin
according to the second preferred embodiment of the present
invention is described in detail as follows:
(1) Preparation of the partially neutralized alkali metal
acrylate
A reactor equipped with a condenser, a dropping funnel and a
stirrer is charged with acrylic acid. An alkali metal hydroxide is
dissolved in water in a beaker separately to form an alkali metal
hydroxide solution. The alkali metal hydroxide solution is fed
dropwise to the reactor through the dropping funnel while being
kept at less than 30.degree. C. and neutralizing 50.about.100% by
mole of the acrylic acid to produce an equivalent amount of an
alkali metal acrylate having the degree of neutralization of
50.about.100% by mole. When the neutralization step is conducted at
a temperature of over 45.degree. C., one of the reactants could be
polymerized.
(2) Inverse suspension polymerization step
A reactor, equipped with a condenser having a Dean-Stark trap, a
pressure-equalizing dropping funnel and a stirrer, is charged with
a surfactant and a hydrocarbon solvent, and then the temperature is
raised to 55.degree..about.60.degree. C. A mixture of the partially
neutralized alkali metal acrylate prepared in step (1) and a water
soluble radical polymerization initiator is fed to the reactor in
small portions, and polymerized completely for about 3 hours.
(3) Azeotropic distilling and surface-crosslinking step
The moisture contained in the resultant polymer is separated by
azeotropic distillation to reduce the water content of the polymer
to about 15 to 45% by weight. When the water content is less than
15% by weight, it is uneconomic. On the other hand, when the water
content is over 45% by weight, the effect of surface-crosslinking
is decreased.
After separating the water from the polymer, the solution of the
crosslinking agent dissolved in methanol (methanol being
10.about.30% by weight, based on the polymer), is added, and the
surface-crosslinking reaction is carried out for 1 hour. The amount
of the crosslinking agent is 0.1.about.2.0% by weight. The reactor
is maintained at room temperature, and then the solvent is removed
by filtration to obtain the polymer.
(4) Coagulating step
After 0.5.about.3.0% by weight of sulfuric acid as a coagulant is
dissolved in 3.about.5 times by weight, based on the polymer, of
methanol, the polymer obtained in step (3) is added thereto and
stirred at room temperature. The solvent is removed by filtration
to collect the coagulate.
(5) Drying step
The resultant coagulate is dried at 120.degree. C. for 1 hour and
passed through a 40-mesh wire gauze to obtain the water absorptive
resin. The water absorption rate of the obtained resin is measured
by the filtering method.
The third preferred embodiment of this invention is a process for
preparing a highly water absorptive resin, which comprises the
following steps:
(a) suspending an aqueous solution of partially neutralized alkali
metal acrylate wherein about 50 to 100% by mole of the carboxyl
groups have been neutralized to their alkali metal salts, and at
least one water soluble radical polymerization initiator, in a
hydrocarbon solvent containing a surfactant having a HLB value of
3.about.6;
(b) subjecting the mixture to inverse suspension
polymerization;
(c) separating the moisture from the produced polymer by azeotropic
distillation to reduce the water content to about 15 to 50% by
weight;
(d) adding a crosslinking agent having three or more reactive epoxy
groups in an amount of 0.01.about.5% by weight based on the
polymer, to subject the polymer of step (c) to
surface-crosslinking; and
(e) subjecting the surface-crosslinked polymer to coagulation with
the use of a coagulant in the presence of an inert solvent, wherein
the amount of the coagulant is 0.01.about.5% by weight based on the
polymer.
The alkali metal acrylate and the water soluble radical
polymerization initiator are the same as described in the foregoing
first preferred embodiment.
As the surfactant, there may be used any surfactant having a HLB
value of 3.about.6, and includes, for example, sorbitan fatty acid
esters such as sorbitan monostearate, and sorbitan monolaurate, and
cellulose esters such as ethyl cellulose, benzyl cellulose,
ethylhydroxy cellulose, cellulose acetate, cellulose butyrate and
cellulose acetate butyrate. Particularly preferred are the sorbitan
fatty acid esters. The surfactant is preferably used in an amount
of 0.5.about.15% by weight based on the monomer used.
As the hydrocarbon solvent used in the inverse suspension
polymerization, there may be used an aliphatic or aromatic
hydrocarbon having a boiling point of 30.degree..about.3200.degree.
C., which includes n-hexane, n-heptane, cyclohexane, and the like.
The preferred solvent is n-hexane. The above-mentioned solvents may
be used alone or in admixture of two or more. The solvent is used
in an amount of preferably 0.1.about.50 parts by weight, more
preferably 0.5.about.30 parts by weight, based on 1 part by weight
of the monomer used.
The moisture-separating process may be carried out during or after
polymerization. A water content of the polymer which is
20.about.50% (by weight based on the polymer), is advantageous in
the surface-crosslinking reaction. On the other hand, when the
water content is out of that range, the water absorptive capacity
and the water absorption rate are lowered to an undesirable
level.
The surface-crosslinking agent used in this invention is water
soluble, and has at least three or more reactive groups such as
epoxy groups which can react with the carboxyl or carboxylate
moiety in a molecule. As the crosslinking agent, there may be used
polyglycidyl ethers, chloroepoxy compounds, polyaldehydes, or the
like. The amount of the surface-crosslinking agent is generally
0.01.about.5% by weight based on the polymer. When the amount is
less than 0.01% by weight, the effect of the surface-crosslinking
agent is insignificant. On the other hand, if the amount of the
surface-crosslinking agent is over 5% by weight, the crosslinking
density is increased such that the water absorptive capacity of the
surface-crosslinked polymer is decreased.
Examples of the inert solvent used in the coagulation step (e)
include lower alcohols such as methanol, ethanol, n-propyl alcohol,
isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl
alcohol or octyl alcohol, or a polyol such as ethylene glycol,
propylene glycol, glycerin or diethylene glycol. The preferred
inert solvent is methanol. The amount thereof is 50.about.500% by
weight, preferably 100.about.300% by weight based on the
polymer.
As the coagulant, there may be used a proton-releasing acid, for
example, sulfuric acid, acetic acid, nitric acid, hydrochloric
acid, and the like. The preferred coagulant is sulfuric acid. The
amount of coagulant to be used depends on the kind of coagulant and
the solvent used, and is generally 0.01.about.3% by weight based on
the inert solvent used.
The fourth preferred embodiment of this invention is a process for
preparing a highly water absorptive resin, which comprises the
following steps:
(a) suspending an aqueous solution of partially neutralized alkali
metal acrylate wherein about 50 to 100% by mole of the carboxyl
groups have been neutralized to their alkali metal salts and at
least one water soluble radical polymerization initiator, in a
hydrocarbon solvent containing a surfactant having a HLB value of
3.about.6;
(b) subjecting the mixture to inverse suspension
polymerization;
(c) adding a crosslinking agent having two or more reactive groups
in an amount which is 0.01.about.5% by weight based on the polymer,
to subject the mixture of step (b) to surface-crosslinking; and
(d) subjecting the surface-crosslinked polymer to coagulation using
a coagulant in the presence of an inert solvent, wherein the amount
of the coagulant is 0.01.about.3% by weight based on the
solvent.
The alkali metal acrylate, the surfactant, the hydrocarbon solvent,
the water soluble radical polymerization initiator, the coagulant
and the inert solvent used in the coagulation are the same as
described in the foregoing third preferred embodiment.
The surface-crosslinking agent uses reactive groups such as epoxy
groups which can react with the carboxyl or carboxylate groups in a
molecule. Examples of the crosslinking agent are polyglycidyl
ethers such as glycerol diglycidyl ether; chloroepoxy compounds
such as epichlorohydrin and .alpha.-methylchlorohydrin;
polyaldehydes such as glyoxal and glutaraldehyde; polyols such as
glycerol and ethylene glycol; polyamines such as ethylenediamine,
and the like. The preferred crosslinking agents are polyglycidyl
ethers. The preferred amount is the same as described in the
foregoing third preferred embodiment.
The fifth preferred embodiment of this invention is a process for
preparing a highly water absorptive resin, which comprises the
following steps:
(a) suspending an aqueous solution of partially neutralized alkali
metal acrylate wherein about 50 to 100% by mole of the carboxyl
groups have been neutralized to their alkali metal salts, and
partially neutralized acrylamido alkane sulfonate (1.about.5% by
weight, wherein about 50 to 100% by mole of the sulfonic groups
have been neutralized to their alkali metal salts), and at least
one water soluble radical polymerization initiator, in a
hydrocarbon solvent containing a surfactant having a HLB value of
8.about.12;
(b) subjecting the mixture to inverse suspension polymerization at
temperatures of 40.degree. to 80.degree. C.;
(c) separating the moisture from the produced polymer by azeotropic
distillation to reduce the water content to about 15 to 45% by
weight;
(d) adding a crosslinking agent, having three or more epoxy groups,
dissolved in methanol, wherein the amount of the crosslinking agent
is 0.1.about.2.0% by weight based on the polymer, to subject the
polymer of step (c) to surface-crosslinking for 1 hour; and
(e) subjecting the product of step (d) to coagulation using a
coagulant in the presence of an inert solvent, and subsequently
drying the resultant coagulate to obtain the water absorptive
resin.
The alkali metal acrylate, the hydrocarbon solvent, the water
soluble radical polymerization initiator, the surface-crosslinking
agent, the coagulant and the inert solvent are the same as
described in the foregoing first preferred embodiment, except that
the amount of the crosslinking agent is preferably 0.1.about.2% by
weight based on the polymer.
According to this invention, the 50.about.100% by mole-neutralized
acrylamido alkane sulfonate which is represented by the following
formula ##STR1## (wherein Z is H or CH.sub.3 ; n is an integer of 0
to 2; and Y is Na, K or Li) is used to improve the water absorption
rate.
The process for preparation of the highly water absorptive resin
according to the fifth preferred embodiment of the present
invention is described in detail as follows:
(1) Preparation of the partially neutralized alkali metal
acrylate
A reactor equipped with a condenser, a dropping funnel and a
stirrer is charged with acrylic acid. An alkali metal hydroxide is
dissolved in water in a beaker to form an alkali metal hydroxide
solution. The alkali metal hydroxide solution is fed dropwise into
the reactor through the dropping funnel while the temperature of
the mixture is kept below 30.degree. C. Approximately 50.about.100%
by mole of the acrylic acid is neutralized to produce an equivalent
amount of an alkali metal acrylate having the degree of
neutralization of 50.about.100% by mole. When the neutralization
step is conducted at a temperature of over 45.degree. C., one of
the reactants could be polymerized.
(2) Inverse suspension polymerization step
A reactor, equipped with a condenser having a Dean-Stark trap, a
dropping funnel, a stirrer and a nitrogen gas inlet pipe, is
charged with a surfactant and a hydrocarbon solvent and the
temperature is raised to 40.degree..about.80.degree. C. A mixture
of the partially neutralized alkali metal acrylate prepared in step
(1), a partially neutralized alkali metal acrylamido sulfonate, and
a water soluble radical polymerization initiator is fed to the
reactor in small portions and the resulting mixture is polymerized
completely.
(3) Azeotropic distilling and surface-crosslinking step
The moisture contained in the polymer of step (2) is separated by
azeotropic distillation to reduce the water content of the polymer
to 15.about.45% by weight.
After separating the water from the polymer, a solution of the
crosslinking agent dissolved in methanol is added and the
surface-crosslinking reaction is carried out for 1 hour. The amount
of the crosslinking agent is preferably 0.1.about.2.0% by weight
based on the polymer.
(4) Coagulating and drying step
The polymer obtained by filtration, after the crosslinking
reaction, is suspended in methanol, and sulfuric acid is added, to
coagulate the polymer. The coagulate is collected by filtration and
dried to obtain the water absorptive resin. The water absorption
rate of the obtained resin is measured by the filtering method
using an 80-mesh wire gauze.
The sixth preferred embodiment of the invention is a process for
preparing a highly water absorptive resin, which comprises the
following steps:
(a) suspending an aqueous solution of partially neutralized alkali
metal acrylate wherein about 50 to 100% by mole of the carboxyl
groups have been neutralized to their alkali metal salts, partially
neutralized acrylamido alkane sulfonate (about 1.about.5% by
weight, wherein about 50 to 100% by mole of the sulfonic groups
have been neutralized to their alkali metal salts), and at least
one water soluble radical polymerization initiator, in a
hydrocarbon solvent containing a surfactant having a HLB value of
3.about.6;
(b) subjecting the mixture to inverse suspension polymerization at
temperatures of 40.degree. to 80.degree. C.;
(c) separating the moisture from the produced polymer by azeotropic
distillation to reduce the water content of the polymer to about 15
to 45% by weight;
(d) adding a crosslinking agent that has three or more reactive
epoxy groups and that is dissolved in methanol (wherein the amount
of the crosslinking agent is 0.1.about.2.0% by weight based on the
polymer), to subject the produced polymer of step (c) to
surface-crosslinking for 1 hour; and
(e) coagulating the product of step (d) using a coagulant in the
presence of an inert solvent, and subsequently drying the resultant
coagulate to obtain the water absorptive resin.
The alkali metal acrylate, the hydrocarbon solvent, the surfactant
solvent, the water soluble radical polymerization initiator, the
coagulant and the inert solvent are the same as described in the
foregoing third preferred embodiment. Additionally, the acrylamido
alkane sulfonate is the same as described in the foregoing fifth
preferred embodiment.
The surface-crosslinking agent may be one that has three or more
reactive epoxy groups; for example, glycerol polyglycidyl ether,
trimethylol propane polyglycidyl ether or sorbitol polyglycidyl
ether. The amount of the crosslinking agent is 0.1.about.2% by
weight based on the polymer.
Water absorptive resin according to the sixth preferred embodiment
is the same as described in the foregoing fifth preferred
embodiment.
The seventh preferred embodiment of the invention is a process for
preparing a highly water absorptive resin, which comprises the
following steps:
(a) suspending an aqueous solution of partially neutralized alkali
metal acrylate (wherein about 50 to 100% by neutralized alkali
metal acrylate (wherein about 50 to 100% by mole of the carboxyl
groups have been neutralized to their alkali metal salts) and at
least one water soluble radical polymerization initiator, in a
hydrocarbon solvent containing a surfactant having a HLB value of
8.about.12;
(b) subjecting the mixture to inverse suspension polymerization
while raising the internal temperature of the reactor successively
to 70.degree. C., to 60.degree..about.67.degree. C., to 70.degree.
C., and then to 75.degree. C., to undergo phase-transition;
(c) during or after the polymerization, separating the moisture
from the produced polymer by azeotropic distillation to reduce the
water content to about 15 to 55% by weight, and then filtering to
remove the solvent;
(d) adding a crosslinking agent that has three or more reactive
epoxy groups and that is dissolved in methanol, wherein the amount
of the crosslinking agent is 0.005.about.15% by weight based on the
produced polymer, to subject the product of step (c) to
surface-crosslinking for 1 to 2 hours at temperatures of 70.degree.
to 85.degree. C.; and
(e) washing the product of step (d) with methanol, filtering, and
drying at temperatures of 90.degree. to 175.degree. C. to obtain
the water absorptive resin.
The present inventors have found a surprising fact that irregularly
shaped, highly water absorptive resins can be obtained by carrying
out polymerization in the presence of a surfactant having a HLB
value of 8.about.12 while raising the reaction temperature
successively to 70.degree. C., to 60.degree..about.67.degree. C.,
to 70.degree. C. and to 75.degree. C., to undergo phase-transition.
These conditions are generally considered to be unsuitable for both
inverse suspension polymerization systems and inverse emulsion
polymerization systems.
Irregularly shaped resins prepared by the method of the present
invention have an increased-surface area. This improves both the
water absorption rate and gel-strength of the resin. Additionally,
in this polymerizing system the viscosity of the resin is suddenly
increased by developing the Trommsdorff effect to conduct
phase-transition.
It is possible to explain this phenomenon, as follows:
(1) one by first occurring phase-transition from a system having
greater mechanical force by agitation than viscous force to another
system wherein mechanical force and viscous force are balanced, and
followed by phase-transition to the system having greater
mechanical force by agitation than viscous force again.
(2) one by first occurring phase-transition from a system (namely
W/O system) wherein main phase is hydrophobic, to a water and oil
equilibrium phase system, and followed by phase-transition to the
hydrophobic system (W/O system) again.
As a result of this phase-transition effect the water absorptive
capacity is further improved due to chemical self-crosslinking in
particles during polymerization, and physical pseudo-crosslinking
by trapped entanglement of the main chain. Moreover, as a result of
raising the polymerization temperature successively as mentioned
above, the shape of polymer is not spherical but irregular.
In this preferred embodiment, the alkali metal acrylate, the
hydrocarbon solvent, the water soluble radical polymerization
initiator and the surface-crosslinking agent are the same as
described in the foregoing first preferred embodiment and the
crosslinking agent is preferably 0.005.about.15% by weight based on
the polymer.
The process for preparation of the highly water absorptive resin
according to the seventh preferred embodiment of the present
invention is described in detail as follows:
(1) Preparation of the partially neutralized alkali metal
acrylate
A reactor, equipped with a condenser, a dropping funnel and a
stirrer, is charged with acrylic acid. An alkali metal hydroxide is
dissolved in water in a beaker to form an alkali metal hydroxide
solution. The alkali metal hydroxide solution is fed dropwise to
the reactor through the dropping funnel while the mixture is kept
below 30.degree. C. The acrylic acid is neutralized, 50-100% by
mole, to produce an equivalent amount of an alkali metal acrylate
having the degree of neutralization of 50.about.100% by mole. When
the neutralization step is conducted at a temperature of over
45.degree. C., one of the reactants could be polymerized.
(2) Inverse suspension polymerization step
A reactor, with the condenser having a Dean-Stark trap, a
pressure-equalizing dropping funnel and a stirrer is charged with a
surfactant and a hydrocarbon solvent, and then the temperature of
the reactor is raised to 70.degree..about.80.degree. C. A mixture
of the partially neutralized alkali metal acrylate prepared in step
(1) and a water soluble radical polymerization initiator are slowly
added to the reactor. The temperature is raised to 70.degree. C.,
then reduced to 60.degree..about.67.degree. C., and raised again to
70.degree. C., and then to 75.degree. C. Clots of gel in irregular
shapes are obtained due to phase-transition.
(3) Azeotropic distilling step
The resultant polymer contains a large amount of water so that it
is difficult for the crosslinking agent to react at the polymer
surface. The moisture contained in the polymer is separated by
azeotropic distillation to reduce the water content of the polymer
to about 15 to 55% by weight. When the water content is less than
15% weight, it is uneconomic. On the other hand, when the water
content is over 55% by weight, the effect of surface-crosslinking
is decreased.
After separating the water from the polymer, the internal
temperature of the reactor is maintained at room temperature. The
solvent is then removed by filtration to obtain the polymer.
(4) Surface-crosslinking step
The polymer produced in step (3) is crosslinked using the
crosslinking agent so as to improve the water absorption rate and
gel-strength. A reactor equipped with a condenser, a stirrer, and a
dropping funnel is charged with a polymer having a water content of
15.about.55% by weight and the solution of the crosslinking agent
and methanol. The surface-crosslinking reaction is carried out at a
temperature of 75.degree. to 80.degree. C. for 1 to 2 hours. The
polymer thus treated is cooled to room temperature and the methanol
is removed by filtration.
(5) Washing and drying step
To remove residual monomers, the obtained polymer is washed twice
with methanol and filtered. The filtered polymer is dried at a
temperature of 90.degree. to 175.degree. C. and passed through a
40-mesh wire gauze to obtain the water absorptive resin in
particles having a uniform size. The water absorption rate and the
water absorptive capacity of the obtained resin is measured by the
filtering method.
The present invention is described in detail by the following
examples, but it should be noted that the invention is not limited
by these examples.
The term "the water absorptive capacity" used in the present
invention means a value determined according to the following
procedure: To 2,000 g of deionized water is added 1 g of the dried
water absorptive resin. Water is absorbed by the polymer for 30
minutes, after which the polymer is collected by filtration with a
80-mesh metallic wire gauze. The volume of the swollen polymer
obtained is measured, and the value is taken as the deionized water
absorption capacity.
The saline solution-absorption rate is a value (g/g) calculated
from the weight of the saline solution (0.9% by weight aqueous
sodium chloride solution) which is absorbed by the polymer for 1, 3
and 5 minutes, respectively.
EXAMPLE 1
A one liter four-necked round-bottomed flask, equipped with a
stirrer, a condenser having a Dean-Stark trap, a pressure
equalizing dropping funnel and a nitrogen gas inlet pipe, was
charged with 200 g of cyclohexane and 2.0 g of Ryoto Sugar Ester
S-970.RTM. (manufactured by Mitsubishi-Kasei Food corporation).
Nitrogen gas was introduced into the flask, so as to remove oxygen
from the flask, and then the flask was heated to 85.degree. C.
Separately, another one liter four-necked round-bottomed flask,
equipped with a stirrer, a condenser and a dropping funnel was
charged with 36 g of acrylic acid. The flask was cooled to room
temperature, and a solution prepared by dissolving 15 g of sodium
hydroxide in 50 g of distilled water was slowly added dropwise,
resulting in an aqueous solution of 75% neutralized sodium
acrylate.
Potassium persulfate (0.32 g) was dissolved thoroughly in 3.88 g of
distilled water and added to the previously prepared sodium
acrylate solution with stirring. This mixture was added dropwise to
the flask containing cyclohexane and the surfactant using the
pressure equalizing dropping funnel over 20 minutes. The reaction
mixture was held at 85.degree. C. for 1 hour to conduct the
polymerization. At the completion of the polymerization, 28 g of
water was removed from the produced polymer by azeotropic
distillation, reducing the water content to 40% by weight.
The mixture was cooled to room temperature, the cyclohexane was
removed by filtration, and the resulting polymer was transferred to
a flask equipped with a condenser, a stirrer and a dropping funnel.
Glycerol polyglycidyl ether (Epok 812, 0.375 g) was dissolved in
200 g of methanol, and the resulting solution was added via
dropping funnel to the flask containing produced polymer. The
resulting mixture was heated to 80.degree. C., and maintained at
that temperature for 1 hour. The flask was then cooled to reduce
the inside temperature of the flask to room temperature, and the
solvent was removed by filtration. The resulting polymer was washed
twice with 40 g of methanol, filtered, and dried at 120.degree. C.
The dried polymer was passed through a 20-mesh wire gauze to obtain
a highly water absorptive resin in particles having a uniform
size.
The results are shown in Table 1.
EXAMPLE 2
A water absorptive resin was prepared in the same manner as
described in Example 1 except that 0.25 g of Epok 812 was used as
the crosslinking agent.
The results are shown in Table 1.
EXAMPLE 3
A water absorptive resin was prepared in the same manner as
described in Example 1 except that 0.425 g of Epok 812 was used as
the crosslinking agent.
The results are shown in Table 1.
EXAMPLE 4
A water absorptive resin was prepared in the same manner as
described in Example 1 except that 0.625 g of Epok 812 was used as
the crosslinking agent.
The results are shown in Table 1.
COMPARATIVE EXAMPLE 1
A water absorptive resin was prepared in the same manner as
described in Example 1 except that the polymer was directly dried
without removing the water.
The results are shown in Table 1.
COMPARATIVE EXAMPLE 2
A water absorptive resin was prepared in the same manner as
described in Example 1 except that 28 g of water was separated from
the polymer to reduce the water content to 40% by weight, prior to
the drying step.
The results are shown in Table 1.
COMPARATIVE EXAMPLE 3
A water absorptive resin was prepared in the same manner as
described in Example 1 except that the crosslinking agent was not
used in the surface-crosslinking step.
The results are shown in Table 1.
TABLE 1
__________________________________________________________________________
Absorptive capacity after 30 minutes Absorption rate in a (g/g
polymer) 0.9% NaCl aqueous In a 0.9% solution (g/g polymer) NaCl
aqueous In distilled gel- 1 min. 3 min. 5 min. solution water
strength*
__________________________________________________________________________
Example 1 83 95 95 98 1124 .smallcircle. Example 2 79 84 85 95 1096
.smallcircle. Example 3 80 88 90 98 1102 .smallcircle. Example 4 82
92 93 99 1115 .smallcircle. Comparative 1 13 25 29 47 512 x
Comparative 2 21 27 35 52 553 Comparative 3 26 32 39 58 611
__________________________________________________________________________
<Note *.smallcircle.: Excellent : Normal x: Poor
EXAMPLE 5
A one liter four-necked round-bottomed flask, equipped with a
stirrer, a condenser having a Dean-Stark trap, a pressure
equalizing dropping funnel and a nitrogen gas inlet pipe, was
charged with 150 g of cyclohexane and 2.0 g of Ryoto Sugar Ester
S-970.RTM. . Nitrogen gas was introduced into the flask to remove
oxygen from the flask, and the flask was then heated to 60.degree.
C.
Separately, another one liter four-necked round-bottomed flask,
equipped with a stirrer, a condenser and a dropping funnel, was
charged with 36 g of acrylic acid. While cooling the flask to room
temperature, a solution prepared by dissolving 15 g of sodium
hydroxide in 50 g of distilled water was added dropwise to produce
an aqueous solution of 75% neutralized sodium acrylate.
Potassium persulfate (0.32 g) was dissolved thoroughly in 3.88 g of
distilled water, added to the previously prepared sodium acrylate
solution and stirred. The mixture was slowly added to the flask
containing cyclohexane and the surfactant using the pressure
equalizing dropping funnel over 1 hour. The mixture was held at
60.degree. C. for 3 hours to conduct the polymerization. At the
completion of the polymerization, 28 g of water was separated from
the produced polymer by azeotropic distillation to reduce the water
content to 40% by weight.
Epok 812 (0.2 g) was dissolved in 10 g of methanol and added to the
polymer through the pressure equalizing dropping funnel. The
reaction was allowed to proceed for 1 hour. After the mixture was
cooled to room temperature, the solvent was removed to obtain the
polymer. Methanol (350 g) and sulfuric acid (1.25 g) were combined
and stirred. The polymer was added and the mixture was stirred to
coagulate. After coagulation, methanol was removed by filtration.
The product obtained was dried at 120.degree. C. for 1 hour, and
passed through a 20-mesh wire gauze to obtain a water absorptive
resin in particles having a uniform size.
The results are shown in Table 2.
EXAMPLE 6
A water absorptive resin was prepared in the same manner as
described in Example 5 except that 2.0 g of sulfuric acid was used
in the coagulation step.
The results are shown in Table 2.
EXAMPLE 7
A water absorptive resin was prepared in the same manner as
described in Example 5 except that 200 g of methanol was used in
the coagulation step.
The results are shown in Table 2.
EXAMPLE 8
A water absorptive resin was prepared in the same manner as
described in Example 5 except that 0.3 g of Epok 812 was used as
the crosslinking agent.
The results are shown in Table 2.
COMPARATIVE EXAMPLE 4
A water absorptive resin was prepared in the same method as
described in Example 5 except that 28 g of water was first
separated from the polymer to reduce the water content to 40% by
weight, prior to the drying step.
The results are shown in Table 2.
COMPARATIVE EXAMPLE 5
A water absorptive resin was prepared in the same method as
described in Example 5 except that sulfuric acid was not used in
the coagulation step.
The results are shown in Table 2.
COMPARATIVE EXAMPLE 6
A water absorptive resin was prepared in the same method as
described in Example 5 except that Epok 812 was not used.
The results are shown in Table 2.
TABLE 2 ______________________________________ Absorption rate in a
0.9% NaCl aqueous solution (g/g polymer) 1 min. 3 min. 5 min.
______________________________________ Example 5 53 55 52 Example 6
51 53 51 Example 7 49 52 52 Example 8 53 54 54 Comparative 4 21 35
41 Comparative 5 34 41 31 Comparative 6 14 31 38
______________________________________
EXAMPLES 9.about.12
A 500 mL four-necked round-bottomed flask, equipped with a stirrer,
a condenser having a Dean-Stark equipment, a dropping funnel and a
nitrogen gas inlet pipe, was charged with 200 Ml of n-hexane and
1.5 g of sorbitan monostearate, and the flask was heated to
65.degree. C. Separately, another flask was charged with 30 g of
acrylic acid and the acid was neutralized with a solution prepared
by dissolving 13.4 g of sodium hydroxide in 39 g of water. The
concentration of the aqueous monomer in the solution was 45% and
the amount of water contained was 55%. Potassium persulfate (0.1 g)
was dissolved therein, and the solution was fed dropwise via
dropping funnel over 30 minutes to the reaction flask containing
the n-hexane solution. Nitrogen gas was introduced into the flask
during the polymerization. Water was removed from the polymer
obtained by azeotropic distillation, reducing the water content to
20%, 30%, 40% and 50% respectively. To each of the resulting
solutions was added an aqueous solution prepared by dissolving 0.08
g of polyglycerol polyglycidyl ether in 1 Ml of water, and stirring
was continued at 70.degree. C. for 3 hours. At the completion of
the polymerization, n-hexane was removed from the polymer. The
polymer was coagulated by addition of 200 g of methanol and 0.2 g
of sulfuric acid.
After coagulation, the methanol was removed, and the polymer was
dried under vacuum at 80.degree. C. to obtain a highly water
absorptive resin.
EXAMPLE 13
A highly water absorptive resin was prepared in the same manner as
described in Example 9 except as follows:
Ethyl cellulose T-50 (1.5 g, manufactured by Hercules Incorporated)
was used instead of sorbitan monostearate. After the
polymerization, the content of water was reduced to 40% by
azeotropic distillation. Polyglycerol polyglycidyl ether (0.1 g,
dissolved in 1 Ml of water) was added to the reaction flask, and
stirring was continued for 2 hours at 70.degree. C. At the
completion of the reaction, n-hexane was removed from the polymer,
and 230 g of methanol and 0.5 g of sulfuric acid were added to the
polymer to effect coagulation.
EXAMPLE 14
A highly water absorptive resin was prepared in the same manner as
described in Example 13 except as follows:
The concentration of aqueous monomer was 35%. After the
polymerization, polyglycerol polyglycidyl ether (0.15 g, dissolved
in 1 Ml of water) was added to the reaction flask and stirred for 3
hours at 75.degree. C. n-Hexane was removed from the polymer, and
250 g of methanol and 0.4 g of sulfuric acid were added to the
polymer to effect coagulation.
COMPARATIVE EXAMPLES 7.about.10
Comparative samples were prepared in the same manner as described
in Example 9 except as follows:
The content of water was reduced to 10% (Comparative Example 7),
15% (Comparative Example 8), 55% (Comparative Example 9) and 60%
(Comparative Example 10) by weight, respectively. After the
polymerization, 0.1 g of polyglycerol polyglycidyl ether dissolved
in 1 Ml of water was added to the reaction flask, and stirred for 2
hours at 70.degree. C. n-Hexane was removed from the polymer, and
200 g of methanol and 0.4 g of sulfuric acid were added to the
polymer to effect coagulation.
COMPARATIVE EXAMPLE 11
Comparative sample 11 was prepared in the same manner as described
in Example 9 except as follows:
The content of water was reduced to 30% by weight. Polyglycerol
polyglycidyl ether (0.1 g) dissolved in 1 Ml of water was added to
the reaction flask, and stirred for 3 hours at 70.degree. C.
COMPARATIVE EXAMPLE 12
Comparative sample 12 was prepared in the same manner as described
in Example 13 except as follows:
The concentration of the aqueous monomer was 35%, and the content
of water after polymerization was 40% by weight. Polyglycerol
polyglycidyl ether (0.1 g, dissolved in 1 mL of water) was added to
the reaction flask, and stirred for 3 hours at 75.degree. C.
The absorption characteristics of the highly water absorptive
resins obtained in Examples 9.about.14 and the comparative samples
obtained in Comparative Examples 7.about.12 are shown in Table 3.
Table 3 illustrates that the polymer of the present invention has
excellent resistance to salts, and a high absorption rate in saline
solution.
TABLE 3 ______________________________________ Absorption rate in
Absorptive saline solution (g/g) capacity in 1 min. 3 min. 5 min.
deionized water (g/g) ______________________________________
Example 9 60 62 62 950 Example 10 59 60 62 920 Example 11 61 62 63
940 Example 12 63 63 63 950 Example 13 60 60 61 930 Example 14 57
57 57 920 Comparative 7 40 42 42 850 Comparative 8 38 38 37 800
Comparative 9 41 41 41 920 Comparative 10 39 41 44 920 Comparative
11 25 27 29 530 Comparative 12 28 30 31 510
______________________________________
EXAMPLES 15.about.17
A 500 mL four-necked round-bottomed flask, equipped with a stirrer,
a condenser having a Dean-Stark trap, dropping funnel and a
nitrogen gas inlet pipe, was charged with 200 mL of n-hexane and 15
g of sorbitan monostearate, and the flask was heated to 65.degree.
C. In another flask, 30 g of acrylic acid was neutralized with a
solution prepared by dissolving 13.4 g of sodium hydroxide in 39 g
of water. The concentration of the aqueous monomer in the solution
was 45% by weight and the amount of water contained was 55% by
weight. Potassium persulfate (0.1 g) was added, and the resulting
solution was added via dropping funnel to the reaction flask
containing the n-hexane solution over about 30 minutes.
Nitrogen gas was introduced to the reaction flask during
polymerization, and the resulting solution was kept at 65.degree.
C. for 2 hours to complete the polymerization. Ethylene glycol
diglycidyl ether (0.08 g, dissolved in 1 mL of water) was added to
the reaction flask and the mixture was kept at 70.degree. C. for 2
hours. After the reaction was complete, n-hexane was removed. The
obtained polymer was added to beakers containing, respectively, 200
g/0.2 g, 200 g/0.5 g and 200 g/1.0 g of methanol and sulfuric acid
to coagulate the polymer. After coagulation, the methanol was
removed, and the resulting polymer was dried under vacuum at
80.degree. C. to obtain a highly water absorptive resin.
EXAMPLE 18
A water absorptive resin was prepared in the same manner as
described in Example 15 except that 1.0 g of ethyl cellulose T-50
was used instead of sorbitan monostearate.
After polymerization was complete, 0.05 g of glycerol diglycidyl
ether dissolved in 1 mL of water was added to the reaction flask,
and the mixture was stirred for 2 hours at 70.degree. C. n-Hexane
was removed, and the polymer obtained was added to a beaker
containing 250 g of methanol and 0.4 g of sulfuric acid to
coagulate the polymer. Methanol was removed, and the resulting
polymer was dried in a vacuum oven at 80.degree. C. to obtain a
highly water absorptive resin.
EXAMPLE 19
A water absorptive resin was prepared in the same manner as
described in Example 18 except that the concentration of monomer in
the aqueous monomer solution was adjusted to 35%. After
polymerization, 0.2 g of polyethylene glycol diglycidyl ether (n=9)
dissolved in 1 mL of water was added to the reaction flask and the
mixture was stirred for 3 hours at 75.degree. C. n-Hexane was
removed, and the polymer was added to a beaker containing 230 g of
methanol and 0.5 g of sulfuric acid to coagulate the polymer.
Methanol was removed, and the resulting polymer was dried in a
vacuum oven at 80.degree. C. to obtain a highly water absorptive
resin.
EXAMPLE 20
A water absorptive resin was prepared in the same manner as
described in Example 18 except that 1.2 g of ethyl cellulose N-100
(manufactured by Hercules Incorporated) was used instead of ethyl
cellulose T-50. After polymerization, 0.09 g of ethylene glycol
diglycidyl ether dissolved in 1 mL of water was added to the
reaction flask, and the mixture was stirred for 2 hours at
70.degree. C. n-Hexane was removed, and the polymer was added to a
beaker containing 200 g of methanol and 1.0 g of sulfuric acid to
coagulate the polymer. Methanol was removed, and the resulting
polymer was dried in a vacuum oven at 80.degree. C. to obtain a
highly water absorptive resin.
COMPARATIVE EXAMPLES 13.about.16
Water absorptive resins were prepared in the same manner as
described in Example 15 except as follows:
After polymerization, 0.08 g of ethylene glycol diglycidyl ether
dissolved in 1 mL of water was added to the reaction flask, and the
concentration of monomer was adjusted to 35%. After polymerization,
0.3 g of polyethylene glycol diglycidyl ether (n=9) dissolved in 1
mL of water was added to the reaction flask, and the mixture was
stirred for 3 hours at 75.degree. C.
COMPARATIVE EXAMPLE 17
A water absorptive resin was prepared in the same manner as
described in Example 20 except that 0.01 g of ethylene glycol
diglycidyl ether dissolved in 1 mL of water was added to the
reaction flask, and the mixture was stirred for 2 hours at
75.degree. C.
The absorption characteristics of the highly water absorptive
resins obtained in Examples 15.about.20 and the samples obtained in
Comparative Examples 13.about.17 are shown in Table 4.
Table 4 illustrates that the polymer of the present invention has
excellent resistance to salts and the high absorption rate in
saline solution.
TABLE 4 ______________________________________ Absorption rate in
Absorptive saline solution (g/g) capacity in 1 min. 3 min. 5 min.
deionized water (g/g) ______________________________________
Example 15 40 43 43 850 Example 16 42 42 43 900 Example 17 41 43 45
930 Example 18 41 41 42 900 Example 19 38 38 40 890 Example 20 43
43 44 950 Comparative 13 21 23 27 510 Comparative 14 23 23 23 540
Comparative 15 20 24 24 530 Comparative 16 18 20 25 500 Comparative
17 22 25 27 530 ______________________________________
EXAMPLE 21
A four-necked round-bottomed flask, equipped with a stirrer, a
condenser having a Dean-Stark trap, a dropping funnel and a
nitrogen gas inlet pipe, was charged with 160 g of cyclohexane and
2.4 g of Ryoto Sugar Ester S-970.RTM. (HLB=9), and the flask was
heated to 60.degree. C. A solution of aqueous sodium acrylate (45%
by weight, 75% neutralized, 80 g) was mixed with an aqueous
solution of 2 g of 2-acrylamido-2-methyl-1-propanesulfonic acid
(which was neutralized with 0.44 g of sodium hydroxide) and 0.1 g
of potassium persulfate. The resulting solution was added dropwise
to the reaction flask. Polymerization was held for about 2 hours at
70.degree. C.
The water was separated from the produced polymer to reduce the
water content to 40% by weight. Epok 812.RTM. (0.12 g) was
dissolved in a little methanol and was added to the polymer and
refluxed for 1 hour.
The polymer obtained was filtered and again dissolved in methanol.
A little sulfuric acid was added to coagulate the polymer. The
coagulated polymer was filtered again, dried, and passed through a
20-mesh wire gauze to obtain a highly water absorptive resin in
particles having a uniform size.
EXAMPLE 22
A water absorptive resin was prepared in the same manner as
described in Example 21 except that only 0.22 g of sodium hydroxide
was used to neutralize 2 g of 2-acrylamido-2-methyl-1-propane
sulfonic acid.
EXAMPLE 23
A water absorptive resin was prepared in the same manner as
described in Example 21 except that 0.66 g of sodium hydroxide was
used to neutralize 3 g of 2-acrylamido-2-methyl-1-propane sulfonic
acid.
COMPARATIVE EXAMPLE 18
A water absorptive resin was prepared in the same manner as
described in Example 21 except that 2-acrylamido-2-methyl-1-propane
sulfonic acid was not used.
COMPARATIVE EXAMPLE 19
A water absorptive resin was prepared in the same manner as
described in Example 21 except that the polymer was not coagulated
by sulfuric acid.
COMPARATIVE EXAMPLE 20
A water absorptive resin was prepared in the same manner as
described in Example 21 except that 2-acrylamido-2-methyl-1-propane
sulfonic acid was not used and the polymer was not coagulated by
sulfuric acid.
The absorptive capacities (in a 0.9% sodium chloride aqueous
solution for 1 minute) of the water absorptive resins prepared in
Examples 21.about.23 and Comparative Examples 18.about.20 are shown
in Table 5.
TABLE 5 ______________________________________ Exam- Exam- Exam-
Compara- Compara- Compara- ple 21 ple 22 ple 23 tive 18 tive 19
tive 20 ______________________________________ 62 65 63 45 50 35
______________________________________ (g/g polymer)
EXAMPLE 24
A four-necked round-bottomed flask, equipped with a stirrer, a
condenser having a Dean-Stark trap, a dropping funnel and a
nitrogen gas inlet pipe, was charged with 160 g of n-hexane and 1.4
g of Ryoto Sugar Ester S-370F.RTM. (HLB value=3), and the flask was
heated to 50.degree. C.
An aqueous sodium acrylate solution (45% by weight, 75%
neutralized, 80 g) was mixed with an aqueous solution prepared from
2 g of 2-acrylamido-2-methyl-1-propane sulfonic acid which was
neutralized with 0.44 g of sodium hydroxide and an aqueous solution
of 0.1 g of potassium persulfate. The resulting solution was added
dropwise to the reaction mixture. Polymerization was conducted for
about 2 hours.
Water was separated from the produced polymer to reduce the water
content to 40% by weight. EPOK 812.RTM. (0.12 g) was dissolved in a
little methanol and was added to the reaction mixture. The solution
was refluxed for 1 hour and the polymer obtained was filtered,
dissolved in methanol, and coagulated by the addition of sulfuric
acid. The coagulated product was filtered, dried, and passed
through a 20-mesh wire gauze to obtain a water absorptive
resin.
EXAMPLE 25
A water absorptive resin was prepared in the same manner as
described in Example 24 except that only 0.22 g of sodium hydroxide
was used to neutralize 2 g of 2-acrylamido-2-methyl-1-propane
sulfonic acid.
EXAMPLE 26
A water absorptive resin was prepared in the same manner as
described in Example 24 except that 0.66 g of sodium hydroxide was
used to neutralize 3 g of 2-acrylamido-2-methyl-1-propane sulfonic
acid.
COMPARATIVE EXAMPLE 21
A water absorptive resin was prepared in the same manner as
described in Example 24 except that 2-acrylamido-2-methyl-1-propane
sulfonic acid was not used.
COMPARATIVE EXAMPLE 22
A comparative sample was prepared in the same manner as described
in Example 24 except that the polymer was not coagulated by
sulfuric acid.
COMPARATIVE EXAMPLE 23
A comparative sample was prepared in the same manner as described
in Example 24 except that 2-acrylamido-2-methyl-1-propane sulfonic
acid was not used and the polymer was not coagulated by sulfuric
acid.
The absorptive capacities (in a 0.9% sodium chloride aqueous
solution for 1 minute) of the resins prepared in Examples
24.about.26 and Comparative Examples 21.about.23 are shown in Table
6.
TABLE 6 ______________________________________ Exam- Exam- Exam-
Compara- Compara- Compara- ple 24 ple 25 ple 26 tive 21 tive 22
tive 23 ______________________________________ 50 55 52 30 40 25
______________________________________ (g/g polymer)
EXAMPLE 27
A one liter four-necked round-bottomed flask, equipped with a
stirrer, a condenser having a Dean-Stark trap, a pressure
equalizing dropping funnel and a nitrogen gas inlet pipe, was
charged with 200 g of cyclohexane and 2.0 g of Ryoto Sugar Ester
S-970.RTM..
Nitrogen gas was introduced into the flask to remove oxygen from
the flask, and then the flask was heated to 75.degree. C. in an oil
bath.
Another one liter four-necked round-bottomed flask, equipped with a
stirrer, a condenser and a dropping funnel, was charged with 36 g
of acrylic acid.
While cooling to room temperature, the acid was 75% neutralized by
the dropwise addition of a solution, prepared by dissolving 15 g of
sodium hydroxide in 50 g of distilled water.
Potassium persulfate (0.12 g) was dissolved thoroughly in 3.88 g of
distilled water, and this solution was mixed with the previously
prepared sodium acrylate solution and stirred. The mixture was
added rapidly to the flask containing cyclohexane and the
surfactant through the pressure equalizing dropping funnel over
about 10 minutes.
The internal temperature of the flask was cycled from 70.degree.
C., to 64.degree. C., to 70.degree. C. again, and to 75.degree. C.
(the temperature of the oil bath was as follows: 85.degree.
C..fwdarw.73.degree. C..fwdarw.85.degree. C..fwdarw.88.degree. C.),
to undergo phase-transition. Thereafter, the temperature of the oil
bath was held to 90.degree. C. for 1 hour to complete the
polymerization. Water (28 g) was separated from the produced
polymer by azeotropic distillation to reduce the water content to
40% by weight. After cooling the flask to room temperature,
cyclohexane was filtered off, and the polymer was introduced to a
flask equipped with a condenser, stirrer and dropping funnel.
Epok 812 (0.375 g) and 200 g of methanol were combined and added
via dropping funnel to the flask containing the polymer. The
temperature was held at 80.degree. C. for 1 hour.
Thereafter, the flask was cooled to room temperature, and the
solution was filtered to obtain the polymer.
The polymer obtained was washed with 40 g of methanol, filtered,
and dried to obtain a water absorptive resin having an irregular
shape. This resin was passed through a 20-mesh wire gauze to obtain
a water absorptive resin in particles having a uniform size.
The results are shown in Table 7. The microphotograph of Example 27
is shown in FIG. 1.
EXAMPLE 28
A water absorptive resin was produced in the same manner as
described in Example 27 except that 0.25 g of Epok 812 was
used.
The results are shown in Table 7.
EXAMPLE 29
A water absorptive resin was produced in the same manner as
described in Example 27 except that 0.425 g of Epok 812 was
used.
The results are shown in Table 7.
EXAMPLE 30
A water absorptive resin was produced in the same manner as
described in Example 27 except that 0.625 g of Epok 812 was
used.
The results are shown in Table 7.
EXAMPLE 31
A water absorptive resin was produced in the same manner as
described in Example 27 except that 36 g of acrylic acid was
neutralized to 70% by adding 14 g of sodium hydroxide in 47.1 g of
distilled water in the polymerization step.
The results are shown in Table 7.
EXAMPLE 32
A water absorptive resin was produced in the same manner as
described in Example 27 except that 36 g of acrylic acid was
neutralized to 65% by adding 13 g of sodium hydroxide in 46.9 g of
distilled water in the polymerization step.
The results are shown in Table 7.
EXAMPLE 33
A water absorptive resin was produced in the same manner as
described in Example 27 except that 36 g of acrylic acid was
neutralized to 60% by adding 12 g of sodium hydroxide in 46.6 g of
distilled water in the polymerization step.
The results are shown in Table 7.
COMPARATIVE EXAMPLE 24
A comparative sample was produced in the same manner as described
in Example 27 except that 28 g of water was first separated from
the polymer to reduce the water content to 40% by weight, followed
by the drying step.
The results are shown in Table 7.
COMPARATIVE EXAMPLE 25
A comparative sample was produced in the same manner as described
in Example 27 except that 28 g of water was first separated from
the polymer to reduce the water content to 40% by weight, and the
polymer was washed twice with 40 g of methanol, followed by the
drying step.
The results are shown in Table 7.
COMPARATIVE EXAMPLE 26
A comparative sample was produced in the same manner as described
in Example 27 except that the temperature of the oil bath was
maintained at 65.degree. C. during the polymerization step.
The results are shown in Table 7 and the microphotograph is shown
in FIG. 2.
COMPARATIVE EXAMPLE 27
A comparative sample was produced in the same manner as described
in Example 33 except that 28 g of water was first separated from
the polymer to reduce the water content to 40% by weight, followed
by the drying step.
The results are shown in Table 7.
TABLE 7
__________________________________________________________________________
Absorptive capacity Absorption rate after 30 minutes in a 0.9
solution (g/g polymer) chloruide aqueous In a 0.9% sod- solution
(g/g polymer) sodium chloride In distilled Gel- Shape of 1 min. 3
min. 5 min. aqueous solution water strength* particle
__________________________________________________________________________
Example 27 74 88 92 94 1107 .smallcircle. irregular Example 28 58
78 82 93 992 .smallcircle. irregular Example 29 57 77 84 87 993
.smallcircle. irregular Example 30 65 87 90 94 1108 .smallcircle.
irregular Example 31 67 80 84 87 911 .smallcircle. irregular
Example 32 63 82 90 100 1402 irregular Example 33 73 105 118 148
1946 irregular Comparative 24 30 66 76 82 840 x irregular
Comparative 25 30 67 79 93 851 x irregular Comparative 26 42 57 61
68 620 spherical Comparative 27 28 42 58 98 970 x spherical
__________________________________________________________________________
<Note *.smallcircle.: excellent : normal x: poor
* * * * *